1. Field of the Invention
The present invention relates to an articulate assembled bent pipe adaptable as a pipe for transportation of powder or slurry in dry or wet state, which is wear resistant and which permits easy partial replacement or repair when it has been worn.
2. Discussion of the Related Art
Pneumatic transporting methods are employed for transporting fine powder coal, clinker, fly ash, casting sand, earth and sand, etc., at iron works, cement factories, thermoelectric power stations and foundaries, etc. Such transporting pipes often sustain severe wear from conveying the media. The wearing is especially conspicuous at the inner surface on the outer bent side of the bent pipe, which is locally eroded in grooves where pitting finally develops, for which repair or total replacement is required.
According to a method generally practiced as a countermeasure against wear of bent pipes for uses of this kind, a bent pipe made of soft steel or carbon steel is used. A box shape reinforcing member is initially attached on the outside of the bent pipe in anticipation of the development of pitting. Then a material which has wear resistance, such as concrete or refractory brick, etc., is prelimilinarily filled in the box, so that the bent pipe may be protected against possible leakage of transport medium by a layer concrete or brick, to prevent material leakage to outside, even if a pit is formed in the bent pipe while in use. This method is undesirable, because the weight of the bent pipe is increased and when the inner surface of the pipe's radially outward bent side is pitted, turbulent flow of transport medium will result, whereby suction force is reduced.
For transport of abrasive media like fly ash or casting sand which cause violent grinding wear, wear resistant cast irons, e.g., high carbon or high chrome cast iron or NI-HARD (trade name) cast iron, etc., have been used and irregular thickness bent pipes with increased thickness at their outer bent side which tends to sustain especially violent abrasion have been manufactured and used. However, even such wear resistant cast irons do not assure long life. When, for example, a bent pipe of high chrome cast iron with its outwardly bent side having a thickness of 30 mm was used in transporting fly ash, pitting developed in approximately 4-6 months.
Once wear resistant cast iron of this type is pitted, its repair by welding is difficult and such welding, if done improperly, might invite cracking and rupture. At present, a leakage proof method of padding the pitted part with a thick plate of soft steel and welding its circumference has been adopted, but after repetition of this method 2-3 times, the pipe body will crack and total replacement will become necessary.
In the case of slurry like pneumatic transport or sand transport by use of pumps, the form of wear by the transport media tends to be erosion or erosion wear which involves local wear. Thus only a very small part of the total weight of the bent pipe will need repair or replacement, resulting in notable bad economy. Accordingly, the development of bent pipes of a material which assures long life and of a construction which permits easy repair is necessary.